As an image forming apparatus such as printers, facsimiles, copiers, plotters, their complex machines, etc., an image forming apparatus using liquid discharge recording methods using a recording head formed of a liquid (droplet) discharge head discharging an ink droplet such as inkjet recorder is known.
The image forming apparatus includes a head tank (sub-tank or buffer tank) feeding an ink to a recording head and including a negative pressure generator generating a negative pressure to prevent the ink from exuding or dripping from a nozzle of the recording head. The head tank includes a flexible (film) member forming a facing of an ink container containing an ink, a negative pressure generator including an elastic member biasing the flexible member outward, and an openable and closable opener for atmosphere opening the ink container up in the air to feed the ink from the ink container to the recording head.
Japanese Patent Nos. 4298474, 4190001 and 4155879 and Japanese published unexamined applications Nos. 2007-015153, 2007-130979, 2008-132638, 2009-023329, 2009-274325 and 2009-023092 disclose that the head tank includes a displacement member (detection member or detection filler) according to a displacement of the flexible member, when the opener for atmosphere is opened to feed the ink from a main tank to the head tank, a carriage is moved to a predetermined detecting position (tank filling position), a driver of the opener for atmosphere included in the apparatus is activated to open up the head tank in the air to fill the ink in the head tank, and a position where a detector of the apparatus detects the displacement member is the tank filling position.
In Japanese published unexamined application No. 2009-023092, in order to feed the ink even while printing, when an ink consumption when printing is not less than a first predetermined value, based on information relative to an ink amount fed from the main tank to the head tank, when the amount is not greater than a second predetermined value, the ink is fed from the main tank to the head tank, and when the amount is greater than the second predetermined value, the ink is not fed from the main tank to the head tank.
Japanese Patent No. 3219326 discloses feeding an ink even while printing with an ink amount detector remaining in the head tank.
As mentioned above, when the head tank includes a displacement member being displaced according to an amount of the ink remaining in the head tank and the filled head tank is detected by the apparatus, the carriage needs to move the predetermined tank filling position where the ink is fed from the main tank to the head tank. Therefore, printing needs stopping when the amount of the ink in the head tank remains less, resulting in low printing speed.
In this case, the ink consumption in the head tank is calculated by counting the number of discharged droplets, and the ink can be fed from the main tank in an amount equivalent to the consumption. However, the tank filling position is not precisely detected, and it is possible that a short feed causes an excessive negative pressure or an excessive feed causes a low negative pressure. Therefore, the carriage needs to be periodically placed at the tank filling detection position to open up the tank in the air, and printing needs stopping, still resulting in low printing speed.
A member or a means required to control feeding the ink to the head tank is thought installed on the carriage, e.g., a detector detecting the amount of the ink remaining in the head tank or a driver driving the opener for atmosphere thereof is equipped on the carriage. However, this increases the weight of the carriage or enlarges the carriage, resulting in enlargement of the apparatus.
Because of these reasons, a need exists for filling the head tank with an ink while printing even when a detector of the apparatus detects the filled tank by detecting a displacement member being displaced according to an amount of the ink remaining in the head tank.